A fluidized bed reactor is a device that injects solid particles therein and injects gas through a plenum and a gas distributor located on a lower portion of the reactor, and changes behavior of the solid particles to be similar that of fluids by making the solid particles float.
Due to improved solid mixing and mass and heat transfer characteristics in comparison with other reactors, a fluidized bed process using such a fluidized bed reactor is widely used in: physical process such as drying, adsorption, cooling, freezing, coating, moving, heat control, filtering, temperature control, etc.; a chemical reaction occurring by a catalytic reaction such as fluid catalytic cracking (FCC), oxychlorination, phthalic anhydride production, polymerization, etc.; a non-catalytic reaction such as coal combustion, coal gasification, calcinations, mineral roasting, waste incineration, etc., and an energy conversion processes.
In the case of a process in which two reactions occur simultaneously, such as a carbon dioxide absorption and regeneration process using a dry regenerable sorbent, an oxidation-reduction process of a chemical-looping combustor, a Fisher-Tropsch process, a sorption enhanced steam methane reforming of natural gas, a chemical-looping hydrogen generation process, etc., two fluidized bed reactors are used and solid conveyance and circulation are required between the two fluidized bed reactors.
As a related-art method used for solid circulation between the two fluidized bed reactors, a fluidized bed solid circulation system shown in FIG. 1A or FIG. 1B is used. FIG. 1A illustrates a solid circulation system including a fast fluidized bed 1 and a bubbling fluidized bed 4, and FIG. 1B illustrates a solid circulation system including a fast fluidized bed 1, a first bubbling fluidized bed 4, and a second bubbling fluidized bed 7.
In the system of FIG. 1A, the fast fluidized bed 1 may be used for both reaction and solid conveyance. A first reaction of two reactions that has a lower reaction rate is performed in the bubbling fluidized bed 4, and the fast fluidized bed 1 is used for another reaction and solid circulation. However, when the reaction rate of the two reactions is low or a sufficient residence time is required, or when there is a limit to a ratio of a gas flow, the two reactions are performed in the first and second bubbling fluidized beds 4 and 7 in which a gas velocity is low, and the fast fluidized bed 1 is additionally used only for solid conveyance as shown in FIG. 1B.
However, when the fast fluidized bed is used as described above, additional gas is required to move up solids by using the fast fluidized bed, and inert (e.g., nitrogen, argon, helium, etc.) should be injected or a steam should be used to facilitate separation from the gas discharged by the reactions. In particular, when the two reactions occur at high temperature and high pressure, gas having high temperature and high pressure should be injected. Therefore, a cost for pre-heating and pressurizing may be additionally incurred. In addition, the gas velocity of the fast fluidized bed should increase to increase the amount of circulated solid, and thus the cost for gas increases further. In addition, when the height over which the solids should go is high, much gas is required.